FIG. 1 shows a prior art low power WLAN processor 102, which is coupled to data bus 101 which delivers data to be transmitted by WLAN processor 102 from data bus 101 to transmit RF output 108. Wireless packets, for example according to one of the IEEE 802.11 family of wireless internetworking standards, including at least 802.11, 802.11a, 802.11b, 802.11g, or 802.11n, and operative at the 2.4 Ghz or 5 Ghz frequency channels, are received on antenna 110, and are passed through transmit-receive (TR) switch 104 to WLAN processor 102 receive RF input 106, where the packets are quadrature mixed with an appropriate 2.4 Ghz or 5 Ghz carrier to baseband, the packet symbol timing is recovered using the preamble part of the packet, header information is recovered from the packet header part of the packet, the payload symbols are demodulated, and the packet payload data is recovered, aggregated with other packet payloads according to packet header information, including the packet source and destination addresses and packet sequence number, and the recovered payload data is delivered to host interface 101 such as to a host computer or other device receiving the recovered WLAN data.
Transmit packets are similarly formed by converting a block of transmit data from interface 101 into packet payloads, modulating the packet payload into baseband symbols according to a packet modulation type, adding a header preceding the payload to form a baseband packet, and quadrature modulating the baseband packet with a 2.4 Ghz or 5 Ghz carrier, amplifying the modulated packet and coupling it to antenna 110 via TR switch 104.
A problem arises in the use of WLAN Processor 102 where the system is operative in an ultra-low power battery environment, and where the WLAN processor 102 powers on infrequently for operation at periodic intervals. One power savings method is to use beacon frames, where the WLAN processor 102 synchronizes to these beacon frames, utilizing a sleep timer to power down at other times, and then powers up some number of beacon frame intervals later to listen for packets requiring response. This method only works when beacon frames are constantly available, and when wake-up intervals are known in advance.
Another method for powering on a WLAN receiver is the utilization of an “out of band” signal, such as a 125 Khz or other low frequency near-field source, where the “out of band” signal is used to wake up the nearby WLAN processor, after which the WLAN processor may send and receive packets. This system has the disadvantage of requiring a separate wake-up signaling mechanism apart from the WLAN communication system. It is desired to provide an external wake-up signal using an ultra low power method which either uses harvested energy or requires a miniscule level of energy to detect a wake-up event and thereafter power-up a WLAN processor 102, using only WLAN signal processing elements.